[PATCH v3 22/35] x86/bugs: Add attack vector controls for mds

David Kaplan
2025-01-08T20:25:52Z

Use attack vector controls to determine if mds mitigation is required.

If cross-thread attack mitigations are required, disable SMT.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
---
arch/x86/kernel/cpu/bugs.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 175dbbf9b06e..298acb80d126 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -476,8 +476,12 @@ static void __init mds_select_mitigation(void)
if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off())
mds_mitigation = MDS_MITIGATION_OFF;

- if (mds_mitigation == MDS_MITIGATION_AUTO)
- mds_mitigation = MDS_MITIGATION_FULL;
+ if (mds_mitigation == MDS_MITIGATION_AUTO) {
+ if (should_mitigate_vuln(X86_BUG_MDS))
+ mds_mitigation = MDS_MITIGATION_FULL;
+ else
+ mds_mitigation = MDS_MITIGATION_OFF;
+ }

if (mds_mitigation == MDS_MITIGATION_FULL) {
if (!boot_cpu_has(X86_FEATURE_MD_CLEAR))
@@ -506,7 +510,8 @@ static void __init mds_apply_mitigation(void)
if (mds_mitigation == MDS_MITIGATION_FULL) {
setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
if (!boot_cpu_has(X86_BUG_MSBDS_ONLY) &&
- (mds_nosmt || cpu_mitigations_auto_nosmt()))
+ (mds_nosmt || cpu_mitigations_auto_nosmt() ||
+ cpu_mitigate_attack_vector(CPU_MITIGATE_CROSS_THREAD)))
cpu_smt_disable(false);
}
}
--
2.34.1